1. Field of the Invention
The present invention relates to a supporting device for supporting or holding an article with the aid of a springy means. More particularly, it relates to a supporting device comprising a springy means in which the apparent spring force can be changed in accordance with the movement or situation of the article to be supported by applying a force to the springy means. The present invention is especially useful when applied to a connection means located between an arm and a hand of an industrial robot.
2. Description of the Prior Art
A supporting device comprising a springy means in which the springy force can be varied in response to the force applied to the article to be supported, is required in various industrial fields. For example, a supporting device is used in a paper feed apparatus. Paper to be fed is pressed onto a paper feeding passage by a spring so as to avoid scattering. The springy force of the supporting device of the prior art is constant irrespective of the kind or number of the paper to be fed. If a stiff spring is chosen so as to deal with thick and hard paper or corrugated paper, thin paper may be torn by the spring. On the other hand, if a soft spring is chosen so as to deal with thin paper, the pressing force thereof is not sufficient for avoiding scattering the thick papers. Therefore, the kind of the paper is limited in accordance with the springy force of the springy means used in the paper feed apparatus, or otherwise the entire springy means should be exchanged to deal with another kind of paper.
A supporting device comprising a springy means is also used in a robot for manufacturing magnetic heads or record player arms. The assembling operation of the magnetic head or record player arm should be carried out accurately and conducted by a weak force so as to avoid damage of the arm or head, which necessities an expensive control means of high accuracy.
Industrial robots are disposed along an assembly line for the automatic production of various articles. For example, an industrial robot is used to insert a rod member into a hole which has a clearance on the order of several microns. In such an insertion operation, the position of the rod member with respect to the hole must be precisely adjusted before insertion of the rod member into the hole so as to achieve smooth insertion thereof and so as to prevent damaging of the rod member and the hole. Therefore, a robot which can easily and precisely position a rod member to be handled in the above-mentioned insertion operation is required.
An industrial robot is used in order to automatically produce articles with a high reliability and at a high speed, which production requires a precise position-control system. The assembling of products with a high accuracy cannot be achieved simply by increasing the accuracy of positioning of the robot itself. An important factor is the ability to accurately adjust relative position between the members to be assembled. This is especially important in a process where a rod member is inserted into a hole of a close clearance of several microns. The robot used in the insertion operation comprises an arm and a hand for gripping the rod member attached to the end of the arm. The rod member is conveyed to a position above the hole by the horizontal movement of the arm. Then the rod member is inserted into the hole by the vertical movement of the arm. The hand of the conventional robot is rigidly secured to the arm end. Therefore, it is impossible to insert the rod member into the hole unless the rod member is precisely aligned with the hole. If the rod member is misaligned with the hole, the rod member and the member to receive the rod member are damaged by the vertical movement of the robot arm for insertion of the rod member. In order to prevent such damaging of the members, a control means for precisely controlling the position of the robot arm is necessary. However, this control means increases the cost of the robot.
There has been proposed a compliance means, comprising a springy means such as a leaf spring or a coil spring, so as to achieve smooth insertion of the rod member into the hole by applying such compliance means to the wrist portion between the hand and the arm of the robot. Such compliance means compensates for the misalignment between the rod member and the hole. If, in a robot having a wrist structure which comprises such a compliance means, the compliance of the wrist is increased so as to increase the compensation for misalignment of the rod member with respect to the hole, the stiffness of the wrist portion for insertion of the rod member into the hole is weakened, with the result that a sufficient insertion force cannot be generated. The large compliance of the wrist portion also causes the rod member grasped by the robot hand to vibrate when the movement of the robot arm is started and stopped. Therefore, the robot cannot be operated at a high speed.
An industrial robot achieving the above mentioned insertion operation and equipped with the compliance device located between the wrist and the hand is also used in the process of manufacturing magnetic discs.
As is illustrated in FIG. 60, a magnetic disc 401 comprises a flat ring plate substrate 402 of aluminum, on which a magnetic layer 403 is formed as a recording medium by a coating method or a sputtering method, the inner periphery 404 of the magnetic disc 401 being uncoated and exposing the aluminum substrate 402. The magnetic disc 401 is assembled with a spindle which is inserted into an opening 420 of the magnetic disc 401 so as to constitute a magnetic disc device. During the process of assembling the magnetic disc device, the magnetic layer 403 of the magnetic disc 401 must not be touched so as to prevent magnetic or mechanical damaging of the magnetic layer 403 and contamination of the disc surface with finger prints or dust.
A conventional hand structure of the robot for handling a magnetic disc is illustrated in FIG. 61. A hand 406 is attached to the end of an arm 405. The hand 406 comprises fingers 406a. Several pieces 407 are provided at the end of the finger 406a. The outer periphery of the magnetic disc 401 is received and held in V-shaped grooves (not shown) in each piece 407 of the finger 406a. This type of conventional hand of the robot is large and heavy, with the result that high speed control cannot be easily achieved. Also, the magnetic disc 401 and the hand 406 may be damaged if the magnetic disc 401 is misaligned with the spindle (not shown) or if the magnetic disc 401 is inclined with respect to the spindle when the spindle is inserted into the opening 420 of the magnetic disc 401. Therefore, the conventional robot necessitates a high accuracy control means for controlling the position and angle of the magnetic disc 401 with respect to the spindle.